The most commonly used means for regulating the supply of ink across the width of a printing press has been the use of a doctor blade acting against a rotating xe2x80x9cfountain rollerxe2x80x9d, which is driven by the press, either with gears or ratchets. The roller and doctor blade form a trough filled with ink, with an adjustable width slit near the bottom and sealing devices at the ends. Additional mechanism must be provided to transfer the ink from the slow-speed fountain roller to the high-speed inking rollers which are transferring ink to the printing plate. The RPM of these inking rollers is in the range of 1500 RPM per minute, while the fountain roller operates at around 10 RPM. One such way of matching the speeds is a xe2x80x9cductor rollerxe2x80x9d which alternately contacts the slow fountain roller and then contacts, and immediately is accelerated by, the high-speed ink rollers. This acceleration and deceleration severely impacts the press components. Another system uses a high-speed knurled inker roller, which is closely spaced to the fountain roller. This knurled roller xe2x80x9cskims-offxe2x80x9d ink on the fountain roller above a certain thickness. These systems are seriously affected by the temperatures of the ink and the press components, by the press speed and by the length of time the press has been running, by wear, by adjustment of the rollers, and by ink rheoscopic variables, among many other things.
Some presses utilize specially designed variable-volume ink pumps. The pump modules are usually in a row across the press, each pump module serving between an inch, and inch-and-a-half of web width.
Ink is a very abrasive liquid which wears-out machine sliding elements such as pistons and valves, and the ink dries hard when exposed to air, adhering mechanisms together. Also, these pumps are expensive, difficult to clean, require maintenance, deviate from set volume, and have many expensive wearing parts which gradually deteriorate over the life of the device, causing leakage and inaccurate control. These drawbacks and other have prevented existing ink pump designs from being widely adopted.
Examples of such prior art are listed:
The Reed U.S. Pat. No. 2,866,411 teaches a central group of variable stroke piston pumps connected by tubes to an ink rail. Distancing the pump from the roller onto which the ink will be dispensed increases cleaning problems.
The Hegeman U.S. Pat. No. 3,018,727 teaches a piston pump with sliding vales. Sliding surfaces immersed in abrasive ink will wear and leak rapidly.
The Fusco U.S. Pat. No. 3,366,051 teaches the use of a plurality of rotary axial-piston variable-volume ink pumps with improved drive.
The Noon U.S. Pat. No. 3,298,305 pumps a steady stream of ink onto a roller. There is a lot of exposure to air and other contaminants.
The Braun U.S. Pat. No. 4,332,196 teaches the use of a series of slide valves which regulate ink volume by timing the xe2x80x9conxe2x80x9d position.
The Bryer U.S. Pat. No. 4,020,760 teaches the use of a variable stroke axial piston pump with a screw acting against a spring to vary the allowable stroke of the piston. There are many parts in this patent that will wear and leak.
The Niemiro U.S. Pat. No. 5,027,706 teaches a time-opening rapidly acting ink valve The varying rheoscopic properties of ink make control in this manner subject to volumetric variations.
The Nikkamen U.S. Pat. No. 5,405,252 teaches the use of a complex diaphragm pump.
The Uera U.S. Pat. No. 5,526,745 teaches a piston pump driven by a stepping motor. This device has many working parts exposed to the abrasiveness of ink.
The Kirihara U.S. Pat. No. 5,575,208 teaches a microprocessor controlled, motor driven, piston type ink pump.
The Ryan U.S. Pat. No. 5,878,667 uses variable ink pressure to control the amount of ink dispensed, which will cause variations in the dispensing rate depending on the temperature and viscosity oif the ink. No provision is shown for regulating the amount of ink dispensed across the width of a roller.
The Atwater U.S. Pat. No. 5,957,051 teaches microprocessor controlled, motor driven, piston type ink pumps which each employ a moving combination piston and rotary valve injector with precision fitted sliding and rotating elements immersed in the abrasive ink; leakage from wear, both internally and externally will occur with use. A blade maintained at a fixed distance from the ink fountain roll serves to spread the ink only if a relatively large amount of ink is being dispensed. Otherwise, only a narrow stream of ink will be applied to the fountain roll. This type of arrangement requires a speed matching arrangement, such as the xe2x80x9cmicrometric roller which may contain a knurled surfacexe2x80x9d mentioned in this patent, which is known to introduce variations in the ink transfer, and to be subject to wear.
The Deschner U.S. Pat. No. 6,085,652 teaches a means of supplying ink to an ink fountain in order to maintain a level of ink in the reservoir, either by a stream of ink falling directly into the reservoir, or onto a slow-moving ink fountain roller which then rotates and moves the ink into the reservoir. A conventional doctor blade controls the thickness of the ink film remaining on the fountain roller which is then transferred to the press by a conventional xe2x80x9cductor rollerxe2x80x9d of a xe2x80x9cmicrometric rollerxe2x80x9d.
Kawata U.S. Pat. No. 6,336,405 teaches yet another variable volume piston pump with moving parts immersed in the abrasive ink.
The present system discloses a digital liquid metering pump wherein the liquid is dispensed responsive to a digital signal or group of signals from a computer, such that the pump output is essentially continuous, and virtually all components in contact with the liquid are disposable.